Drosophila, like many poikilothermal animals, is able to acclimate to extreme environmental temperatures. The purpose of this study is to determine the metabolic changes that occur during temperature acclimation in Drosophila and to identify some of the genetic and metabolic factors that influence the capacity of the animal to acclimate. Metabolic patterns during temperature acclimation will be assessed by in vitro and in vivo determinations of glycolytic, pentose shunt cycle, and Krebs cycle activities and glycogen, nucleic acid, lipid and protein biosyntheses using radioisotope procedures. Genetic influences on the temperature acclimation process will be examined by altering the gene dosage of the X-chromosome genes for glucose-6-phospate dehydrogenase, Zw, and 6-phosphogluconate dehydrogenase, Pgd, in the genomes of male and female D. melanogaster and comparing the capacities of flies with altered genomes to acclimate with that of wild-type individuals. Furthermore, the effects of metabolic disruption due to the presence of mutant genes, such as the null mutants of the Zw and Pgd loci, in the genome on temperature acclimation will be studied. In addition, the role of allelozyme polymorphism in determining fitness to different environmental temperatures for individuals of natural and artificial populations will be evaluated by electrophoretic procedures.